It is often medically necessary or advisable to remove hard matter, such as kidney stones, gallstones, or foreign bodies from the body of a patient to avoid adverse effects including pain, infection and blockage of body lumens. Removal of hard matter can be done by open surgery, but it is preferable to remove hard matter by minimally-invasive means when possible. Non-invasive removal of hard matter generally involves advancing a specialized device such as a ureteroscope, endoscope, or laparoscope (any or all of which are referred to generally as a “scope”) to the location of the hard matter and either retrieving it using a retrieval device such as a stone retrieval basket or pulverizing it by applying energy to the hard matter with, for example, a laser (termed “lithotripsy”).
When hard matter is pulverized within a body lumen of a patient, however, the fragments of the hard matter may migrate away from the energy source (termed “retropulsion”). Stone fragments that migrate away from sites of lithotripsy can act as nuclei for the formation of new calculi or concretions and can cause other complications. To minimize the risk of fragment migration, it has become common in lithotripsy procedures to deploy an antiretropulsion device such as the BackStop® polymer system commercialized by Pluromed, Inc. (Woburn, Mass.) and sold by Boston Scientific Corporation (Natick, Mass.). However, the use of antiretropulsion devices inevitably adds time and complexity to lithotripsy procedures. As the average cost of operating room time in the US is $15-$25 per minute, there is an ongoing need to minimize the complexity and time required to deploy and retrieve antiretropulsion devices. (Stahl, J et al., Reorganizing patient care and workflow in the operating room: a cost-effectiveness study, Surgery, 139:717-728, 2006.)